This invention generally relates to spectroscopic studies and, more particularly, to inductively coupled plasma tubes used for sample excitation and spectroscopic studies. plasma sample 10,000
Plasma discharges are frequently used to heat a sample material for spectroscopic studies. The spectra of the known plasma gas can be subtracted from the overall spectrum in order to derive the sample spectrum. Plasma heating requires a relatively high-power Plasma and a plasma with little noise is required to isolate the sample spectrum. Flowing gas streams have been inductively heated to generate plasmas effective to atomize. ionize and/or excite samPle materials for mass spectroscopy studies, where typical plasma temperatures are in the range of 4,000 to 10,000 K.
While argon and helium are conventional gases used in such inductively coupled (ICP) plasmas, other gases may be selected for noninterference with the expected sample spectrum i.e.; gases such as neon, xenon, krypton, hydrogen, nitrogen, oxygen, carbon dioxide, and ethylene. The capability of selecting from a variety of gases to form the plasma enables the plasma density and temperature range, which are inversely proportional to the ionization potential of the gas, to be varied. It will be appreciated, however, that a plasma jet of some gases, e.g., hydrogen, can be dangerous or may consume quantities of expensive gases i.e., xenon. Illustrative plasma generators are discussed in U.S. Pat. No. 4,473,736. "Plasma Generator", issued Sept. 25, 1984, to Bloyet et al.. and 4,482.246. "Inductively Coupled Plasma Discharge in Flowing Non-Argon Gas at Atmospheric Pressure for Spectrochemical Analysis." issued Nov. 13, 1984, to Meyer et al.
Electrodeless discharge lamps provide a relatively low noise light source and have been used in some spectroscopic systems. However such lamps generally operate at low power and cannot always be used in spectroscopic studies. A discussion of electrodeless discharge lamps and other conventional discharge devices is found in U.S. Pat. No. 4,266,166, "Compact Fluorescent Light Source Having Metallized Electrodes," issued May 5, 1981 to Proud et al.
In accordance with the present invention an inductively coupled plasma is generated in a closed torch for operation at relatively high power (i.e. up to about 1 kW) and low noise for application to a variety of spectroscopic studies. Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.